JP2000058127A - Polymer lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery superior in mass productivity and having a high discharge capacity, when it is discharged at a high rate by providing a negative electrode containing a two-dimensional porous body having the tensile strength and numerical aperture of specific ranges and made of copper or a copper alloy as a current collector. SOLUTION: The tensile strength of a two-dimensional porous body made of copper or a copper alloy is set to 4 N/mm2 or above, and the numerical aperture is set to 40-80%. Positive electrode layers 5 are carried on both faces of a negative electrode current collector 6 made of this two-dimensional porous body to form the positive electrode 1 of a polymer lithium secondary battery. Negative electrode layers 7 are carried on both faces of the negative electrode current collector 6, made of the two-dimensional porous body to form a negative electrode 2. The positive electrode current collector 4 of the positive electrode 1 is extended into a band shape to form a band-like positive electrode terminal 8, and the negative electrode current collector 6 of the negative electrode 2 is extended into a band shape to form a band-like negative electrode terminal 9. A layered product constituted of the positive electrode 1, negative electrode 2 and an electrolyte layer 3 is sealed in an outer packaging film 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polymer lithium secondary battery having an improved negative electrode.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a non-aqueous electrolyte secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged. Such a secondary battery includes a negative electrode using lithium or a lithium alloy as an active material, a positive electrode containing an oxide, sulfide, or selenide such as molybdenum, vanadium, titanium, or niobium as an active material, and a nonaqueous electrolyte. There is known a lithium secondary battery including:

In recent years, a negative electrode containing a carbonaceous material that absorbs and releases lithium ions, such as coke, graphite, carbon fiber, a resin fired body, and pyrolytic gas phase carbon, has been used as a negative electrode. The development and commercialization of lithium ion secondary batteries using lithium and lithium manganese oxide-containing batteries are being actively pursued.

Meanwhile, in order to further reduce the weight and size of the secondary battery, for example, US Pat.
As disclosed in US Patent No. 6,318, a polymer lithium secondary battery has been developed. The polymer lithium secondary battery includes a sheet-shaped positive electrode, a sheet-shaped negative electrode, and an electrolyte layer interposed between the positive electrode and the negative electrode. The secondary battery is manufactured by, for example, a method described below. First, a positive electrode, a negative electrode and an electrolyte layer containing a plasticizer such as DBP (dibutyl phthalate) which can be removed later and not impregnated with a non-aqueous electrolyte are prepared. Laminating the obtained positive electrode and negative electrode with an electrolyte layer interposed therebetween,
For example, they are integrated by thermocompression bonding. Subsequently, after removing the plasticizer in the laminate by, for example, solvent extraction, the battery is manufactured by impregnating with a non-aqueous electrolyte and sealing the obtained power generation element with an exterior material.

By the way, the above-mentioned negative electrode not impregnated with a non-aqueous electrolyte solution contains, for example, the plasticizer, a binder such as a copolymer of vinylidene fluoride [VdF] and hexafluoropropylene [HFP], and lithium ions. A paste is prepared by kneading an active material such as a carbonaceous material that absorbs and releases in the presence of a solvent, and the paste is applied to a two-dimensional porous body, dried, and pressed by a rolling roll. Is done. As the two-dimensional porous body, copper expanded metal or copper punched metal is used.

[0006]

However, in the case where a two-dimensional porous body is used as the current collector and the tensile strength of the two-dimensional porous body is low in the negative electrode produced by the above-described method, pressing is performed with a rolling roll. In this case, since the elongation rate of the two-dimensional porous body is large, wrinkles occur in the paste layer applied to the two-dimensional porous body, or cracks occur when the elongation percentage is extremely large, which impairs mass productivity. There is a problem. Further, in order to improve this problem, when the porosity of the two-dimensional porous body is reduced to increase the tensile strength,
Since the lithium ion mobility of the negative electrode decreases, the discharge capacity of the polymer lithium secondary battery including the negative electrode when discharged at a high rate decreases.

An object of the present invention is to provide a polymer lithium secondary battery which is excellent in mass productivity and has a high discharge capacity when discharged at a high rate.

[0008]

The polymer lithium secondary battery according to the present invention has a tensile strength of 4 N / mm ² or more, a porosity of 40 to 80%, and a two-dimensional structure of copper or copper alloy. A negative electrode including a porous body as a current collector is provided.

Another polymer lithium secondary battery according to the present invention is obtained by a method in which a paste containing an active material and a polymer having a property of retaining a nonaqueous electrolyte is applied to a current collector and pressed. In a polymer lithium secondary battery provided with a negative electrode, the current collector has a tensile strength of 4N.
/ Mm ² or more, a porosity of 40 to 80%, and a two-dimensional porous body made of copper or a copper alloy.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an example of a polymer lithium secondary battery according to the present invention will be described with reference to FIG.

That is, a polymer lithium secondary battery is:
A positive electrode 1, a negative electrode 2, and a gel electrolyte layer 3 disposed between the positive electrode 1 and the negative electrode 2 are provided. The positive electrode 1
Has a structure in which a positive electrode layer 5 is supported on both surfaces of a current collector 4 made of, for example, a two-dimensional porous body. On the other hand, the negative electrode 2
Are negative electrode layers 7 on both surfaces of a current collector 6 made of a two-dimensional porous body.
Is carried. The strip-shaped positive electrode terminal 8 is obtained by extending the two-dimensional porous body 4 of each of the positive electrodes 1 into a strip shape. On the other hand, the strip-shaped negative electrode terminal 9 is obtained by extending the two-dimensional porous body 6 of the negative electrode 2 into a strip shape. Positive electrode lead 10
Are connected to the two positive terminals 8. A negative lead (not shown) is connected to the negative terminal 9. The laminate composed of the positive electrode 1, the negative electrode 2, and the electrolyte layer 3 has a structure in which the positive electrode lead 10 and the negative electrode lead extend from the film 11 in an exterior film 11 having a barrier function against moisture, air, and the like. Sealed.

As the positive electrode, the negative electrode, and the electrolyte layer of the polymer lithium secondary battery, for example, those described below can be used.

(Positive Electrode 1) In the positive electrode 1, a positive electrode layer 5 containing a positive electrode active material, a non-aqueous electrolyte and a binder for holding the electrolyte is supported on both surfaces of a current collector 4 such as a two-dimensional porous body. It has the structure which was done.

Examples of the positive electrode active material include various oxides (eg, lithium-manganese composite oxide such as LiMn ₂ O ₄ , manganese dioxide, lithium-containing nickel oxide such as LiNiO _2, and lithium-containing cobalt oxide such as LiCoO ₂ , for example). Oxide, lithium-containing nickel-cobalt oxide, lithium-containing amorphous vanadium pentoxide and the like, and chalcogen compounds (for example, titanium disulfide and molybdenum disulfide). Among them, it is preferable to use a lithium manganese composite oxide, a lithium-containing cobalt oxide, and a lithium-containing nickel oxide.

The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.

Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and dimethyl carbonate (D
MC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (γ-
BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran and the like. The non-aqueous solvents may be used alone or as a mixture of two or more.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (L
iPF _6), boric tetrafluoride lithium (LiBF _4), lithium hexafluoroarsenate (LiAsF _6), lithium salts such as lithium trifluoromethane sulfonate (LiCF ₃ SO ₃₎ may be mentioned.

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.2 mol / l to 2 mol / l.

The binder has a property of retaining a non-aqueous electrolyte. Examples of such a binder include a polyethylene oxide derivative, a polypropylene oxide derivative, a polymer containing the derivative, polytetrafluoropropylene, a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP), and polyvinylidene fluoride ( PVdF) or the like can be used. Among them, a VdF-HFP copolymer is preferred.

The positive electrode may include a conductive material from the viewpoint of improving conductivity. Examples of the conductive material include artificial graphite, carbon black (eg, acetylene black), nickel powder, and the like.

As the two-dimensional porous body as the current collector, a mesh made of aluminum or an aluminum alloy, an expanded metal, a punched metal, or the like can be used. Examples of the aluminum alloy include an aluminum-nickel alloy, an aluminum-titanium alloy, and an aluminum-iron alloy. The current collector of the positive electrode is not limited to such a two-dimensional porous body, and for example, an aluminum foil can be used.

The reason why the tensile strength of the two-dimensional porous body is defined within the above range is as follows.
If the tensile strength is less than 5 N / mm ² , the elongation of the two-dimensional porous body in the pressing step described later may increase, so that the positive electrode layer may be wrinkled or cracked. / Mm ² or more, more preferably 50 N / mm ² or more.

The porosity of the two-dimensional porous body is defined in the above range for the following reason. If the porosity is less than 40%, the lithium ion mobility of the positive electrode may decrease, and the high-rate discharge capacity of the polymer lithium secondary battery may decrease. On the other hand, when the porosity is 8
If it exceeds 0%, the tensile strength of the two-dimensional porous body is 5N.
/ Mm ² . A more preferable range of the porosity is 55 to 70%.

As the positive electrode terminal, a two-dimensional porous body extending in a band shape as described with reference to FIG. 1 can be used, and a band-like aluminum foil is connected to the two-dimensional porous body. This may be used as a positive electrode terminal.

The positive electrode lead can be formed of, for example, an aluminum foil.

(Negative Electrode 2) The negative electrode 2 has a structure in which a negative electrode layer 7 containing a negative electrode active material, a non-aqueous electrolyte and a binder holding the electrolyte is supported on a current collector 6 formed of a two-dimensional porous body. Having. The two-dimensional porous body is made of copper or a copper alloy, has a tensile strength of 4 N / mm ² or more, and has a porosity of 40 to 80%.

Examples of the negative electrode active material include carbonaceous materials that occlude and release lithium ions. Such carbonaceous materials include, for example, those obtained by firing organic polymer compounds (eg, phenolic resin, polyacrylonitrile, cellulose, etc.), those obtained by firing coke and mesophase pitch, and those made by artificial graphite. And carbonaceous materials represented by natural graphite and the like. Among them, it is preferable to use a carbonaceous material obtained by firing the mesophase pitch at a temperature of 500 ° C. to 3000 ° C. in an inert gas atmosphere such as an argon gas or a nitrogen gas under normal pressure or reduced pressure.

As the non-aqueous electrolyte, those similar to those described above for the positive electrode are used.

The binder has the property of retaining a non-aqueous electrolyte. As the binder, a polymer of the same type as that described for the positive electrode described above can be used, and among them, a VdF-HFP copolymer is preferable.

As the two-dimensional porous body as the current collector, a mesh made of copper or a copper alloy, an expanded metal, a punched metal, or the like can be used. Examples of the copper alloy include a copper-nickel alloy and a copper-titanium alloy. Among the two-dimensional porous bodies described above,
Punched metal is preferred.

The tensile strength of the two-dimensional porous body is 4
It is preferred to be N / mm ² or more. This is due to the following reasons. The tensile strength is 4 N / m
If it is less than m ² , the elongation rate of the two-dimensional porous body in the pressing step described later increases, so that wrinkles and cracks occur in the negative electrode layer, and mass productivity decreases. The tensile strength is 8N
/ Mm ² or more, more preferably 40 N / mm ² or more.

The porosity of the two-dimensional porous body is 40 to 8
Preferably, it is in the range of 0%. This is due to the following reasons. When the porosity is less than 40%, the lithium ion mobility of the negative electrode is reduced, so that the discharge capacity of the polymer lithium secondary battery at a high rate is reduced. On the other hand, when the porosity exceeds 80%, the tensile strength of the two-dimensional porous body becomes smaller than 4 N / mm ² .
A more preferable range of the porosity is 55 to 70%.

As the negative electrode terminal, a two-dimensional porous body extending in a band shape as described with reference to FIG. 1 can be used, and a band-like copper foil is connected to the two-dimensional porous body. This may be used as a negative electrode terminal.

The negative electrode lead can be formed, for example, from a copper foil.

(Electrolyte Layer) This electrolyte layer contains a non-aqueous electrolyte and a binder for holding the electrolyte.

As the non-aqueous electrolyte, those similar to those described above for the positive electrode are used.

The binder has a property of retaining a non-aqueous electrolyte. As the binder, a polymer of the same type as that described for the positive electrode described above can be used, and among them, a VdF-HFP copolymer is preferable.

From the viewpoint of further improving the strength, the electrolyte layer may contain organic particles or inorganic particles such as silicon oxide powder.

The polymer lithium secondary battery is manufactured, for example, by the method described below. Including a plasticizer,
A positive electrode not impregnated with the nonaqueous electrolyte, a negative electrode containing the plasticizer and not impregnated with the nonaqueous electrolyte, and an electrolyte layer containing the plasticizer and not impregnated with the nonaqueous electrolyte are prepared. The positive electrode and the negative electrode are laminated with the electrolyte layer interposed therebetween, and integrated by thermocompression bonding. The plasticizer is removed from the obtained laminate by, for example, solvent extraction, impregnated with a non-aqueous electrolyte, and then sealed with an exterior film to obtain the secondary battery.

The plasticizer has excellent compatibility with the binder and can impart flexibility to the positive electrode, the negative electrode or the electrolyte layer, and can melt the positive electrode, the negative electrode or the electrolyte layer during thermocompression bonding. It is preferable that the material has the four properties that it can be easily removed. Examples of the plasticizer include dibutyl phthalate (DBP), dimethyl phthalate (DMP), and ethyl phthalyl ethyl glycolate (EPEG).

The positive and negative electrodes and the electrolyte layer containing a plasticizer and not impregnated with a non-aqueous electrolyte are prepared, for example, by the method described below.

<Preparation of Positive Electrode Containing a Plasticizer and Not Impregnated with Nonaqueous Electrolyte>
After preparing a paste by mixing the polymer having the property of retaining the nonaqueous electrolyte, the conductive material and the plasticizer in an organic solvent such as acetone, applying the paste to the current collector, and drying the paste. For example, the active material, the polymer having the property of retaining the non-aqueous electrolyte, the conductive material, and the plasticizer in an organic solvent such as acetone. To prepare a paste, prepare a non-aqueous electrolyte-unimpregnated positive electrode sheet by forming a film, and bond the obtained positive electrode sheet and the current collector by, for example, thermocompression bonding. .

<Preparation of a Negative Electrode Containing a Plasticizer and Not Impregnated with a Nonaqueous Electrolyte> The negative electrode may be formed, for example, by mixing the active material, a polymer having a property of retaining the nonaqueous electrolyte, and the plasticizer with acetone or the like. To prepare a paste, apply the paste to the two-dimensional porous body, dry the paste, and press it with, for example, a rolling roll.

<Preparation of Electrolyte Layer Containing Plasticizer and Not Impregnated with Nonaqueous Electrolyte> For example, the electrolyte layer is made of a polymer having the property of retaining the nonaqueous electrolyte and an organic solvent such as acetone. It is produced by preparing a paste by mixing in a solvent and forming the paste into a film.

In the solvent extraction, it is preferable to apply ultrasonic waves to the solvent or reduce the pressure of the atmosphere. The solvent used is not particularly limited as long as it does not easily damage the battery material and has good compatibility with the plasticizer. For example,
Organic solvents such as alcohols and saturated hydrocarbon compounds are preferred. Among them, a saturated hydrocarbon compound is preferable. As such a saturated hydrocarbon compound, those having 5 to 12 carbon atoms are preferable. Saturated hydrocarbon compounds having a carbon number within the above range are inexpensive, easily available, and easy to recycle and reuse. Since a saturated hydrocarbon compound having less than 5 carbon atoms exists as a gas at normal temperature (around 25 ° C.), handling may be difficult. On the other hand, a saturated hydrocarbon compound having a carbon number of more than 12 has a high viscosity of the liquid, so that the permeability of the solvent to the positive electrode, the negative electrode and the electrolyte layer not impregnated with the electrolytic solution may be reduced. More preferred saturated hydrocarbon compounds have 7 to 10 carbon atoms and are straight-chain ones.

As described in detail above, the polymer lithium secondary battery according to the present invention has a tensile strength of 4 N / mm ² or more, a porosity of 40 to 80%, and a two-dimensional structure of copper or copper alloy. A negative electrode including a porous body as a current collector is provided. Such a negative electrode has high mobility of lithium ions and can prevent wrinkles and cracks from being generated in the negative electrode layer supported on the current collector. As a result, a polymer lithium secondary battery having a high discharge capacity at a high rate and excellent mass productivity can be provided.

Further, another polymer lithium secondary battery according to the present invention is obtained by a method of applying a paste containing an active material and a polymer having a property of retaining a nonaqueous electrolyte to a current collector and pressing the paste. A negative electrode, wherein the current collector has a tensile strength of 4 N / mm ² or more and a porosity of 40 to 80;
% And a two-dimensional porous body made of copper or a copper alloy. Such a negative electrode can reduce the rate of elongation of the two-dimensional porous body during pressing, so that wrinkles and cracks can be suppressed in the paste applied to the two-dimensional porous body. Further, the negative electrode has a high lithium ion mobility. Therefore, the polymer lithium secondary battery provided with the negative electrode can simultaneously satisfy excellent mass productivity and high discharge capacity at a high rate.

[0048]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments according to the present invention will be described below in detail with reference to the drawings.

(Examples 1 to 3) <Preparation of positive electrode not impregnated with non-aqueous electrolyte> As an active material, 56% by weight of a lithium manganese composite oxide represented by a composition formula of LiMn ₂ O ₄ and carbon black of 5% were used. % By weight, and 17% by weight of a vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder as a binder.
And 22% by weight of dibutyl phthalate (DBP) were mixed in acetone to prepare a paste. The obtained paste is applied to both sides of an aluminum expanded metal having a thickness of 40 μm, dried, passed through a hot rolling roll once, pressed, and cut to produce a positive electrode not impregnated with a non-aqueous electrolyte. did. In addition, in the positive electrode, the one obtained by extending the expanded metal made of aluminum into a band shape was used as a positive electrode terminal.

<Preparation of Negative Electrode Not Impregnated with Nonaqueous Electrolyte> After pulverizing mesophase pitch carbon fiber as an active material,
58% by weight of powder heat-treated at ℃ and Vd as binder
A paste was prepared by mixing 17% by weight of the F-HFP copolymer powder and 25% by weight of dibutyl phthalate (DBP) in acetone. The obtained paste has a width of 108 mm and a thickness of 270 to 280 μm on both sides of a copper expanded metal (having a width of 130 mm and a thickness of 50 μm) whose tensile strength and porosity are the values shown in Table 1 below. After being coated and dried as described above, it was passed through a hot rolling roll once, pressed, and cut to obtain a non-aqueous electrolyte-unimpregnated negative electrode. In the negative electrode, a copper expanded metal extended in a strip shape was used as a negative electrode terminal. Further, the measurement of the tensile strength is performed by measuring the current collector substrate with a width of 10 mm.
mm, length 70 mm, each end of 10
mm at a speed of 1 mm / min.

<Preparation of Electrolyte Layer>
3 parts by weight, 22.2 parts by weight of a VdF-HFP copolymer powder as a binder, and dibutyl phthalate (DBP)
44.5 parts by weight were mixed in acetone to form a paste. The obtained paste was applied on a PET film, formed into a sheet, and cut to form an electrolyte layer not impregnated with a non-aqueous electrolyte.

<Preparation of Nonaqueous Electrolyte> A nonaqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 2: 1 was mixed with LiPF ₆ as an electrolyte at a concentration of 1 mol / mol. 1 to prepare a non-aqueous electrolyte.

<Battery Assembly> Two non-aqueous electrolyte impregnated positive electrodes were
Sheets, one non-aqueous electrolyte impregnated negative electrode and two non-aqueous electrolyte non-impregnated electrolyte layers were prepared, and these were laminated so that the electrolyte layer was interposed between the positive electrode and the negative electrode. Then, a unit cell not impregnated with a non-aqueous electrolyte was prepared by heat-pressing with a heated rigid roll.

Such a unit cell was immersed in n-decane and left with stirring with a magnetic stirrer. This operation was repeated until the concentration of DBP in n-decane by gas chromatography became 20 ppm or less, thereby removing the plasticizer in the unit cell. After drying the laminate, a positive electrode lead was connected to a positive terminal of the unit cell, and a negative electrode lead was connected to a negative terminal. The unit cell is impregnated with a non-aqueous electrolyte having the above composition, and polyethylene terephthalate (P
ET) After sealing with an exterior film consisting of a laminated film in which a film, an aluminum foil and a heat-attached resin film are laminated in this order, 45 m in an atmosphere of 20 ° C.
By charging the battery to 4.2 V with a current of A (0.5 C), the theoretical capacity having the structure shown in FIG.
An Ah polymer lithium secondary battery was manufactured.

(Example 4) Except for using a copper punched metal (having a width of 130 mm and a thickness of 20 µm) having a tensile strength and a porosity shown in Table 1 below as a current collector of a negative electrode. Then, the same polymer lithium secondary batteries as those in Examples 1 to 3 described above were manufactured.

(Comparative Example 1) A copper expanded metal (width: 130 mm, thickness: 50 μm) having a tensile strength and a porosity shown in Table 1 below was used as a current collector of the negative electrode. Polymer lithium secondary batteries similar to those of Examples 1 to 3 described above were manufactured.

Comparative Example 2 Except for using a copper punched metal (having a width of 130 mm and a thickness of 20 μm) having a tensile strength and an opening ratio shown in Table 1 below as a current collector of a negative electrode. Then, the same polymer lithium secondary batteries as those in Examples 1 to 3 described above were manufactured.

For the negative electrodes of the secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2, paste was applied to a two-dimensional porous body,
When the paste layer was dried and hot pressed, it was examined whether wrinkles or cracks occurred in the paste layer by the method described below. That is, a paste having the same composition as described above is prepared,
The obtained paste was applied to both sides of each current collector to the same width and thickness as described above, dried, cut into 1 m lengths, passed through a hot rolling roll once and pressed. . The surface of the paste after this pressing was visually observed, and the length of the negative electrode was 1
The number of wrinkles and the number of cracks per m were measured, and the results are shown in Table 1 below.

Further, the obtained secondary batteries of Examples 1 to 4 and Comparative Examples 1 and 2 were discharged at a constant current of 18 mA (0.2 C) in a 20 ° C. atmosphere to a terminal voltage of 3.0 V. After discharging, the discharge capacity (C _0.2C ) was measured.
Next, the battery was charged to 4.2 V with a current of 45 mA (0.5 C), and then discharged to a terminal voltage of 3.0 V with a constant current discharge of 45 mA (0.5 C). Furthermore, 45mA (0.5C)
After charging to 4.2 V with a current of 90 mA (1.0 mA
C) The _battery was discharged to a terminal voltage of 3.0 V by the constant current discharge, and the discharge capacity (C _1.0C ) at this time was measured. And 18mA
The discharge capacity (C) of the constant current discharge of 90 mA (1.0 _C ) with respect to the discharge capacity (C 0.2C) of the constant current discharge of ( _{0.2 C} )
_1.0C ), and the average value is shown in Table 1 below.

[0060]

[Table 1]

As is clear from Table 1, Example 1 was provided with a negative electrode having as a current collector a two-dimensional copper porous body having a tensile strength of 4 N / mm ² or more and a porosity of 40 to 80%. The secondary batteries of Nos. 1 to 4 are the secondary batteries of Comparative Example 1 including a negative electrode including a two-dimensional porous body having a tensile strength smaller than the above range and a porosity larger than the above range as a current collector. In comparison, it can be seen that the rate of occurrence of wrinkles and cracks in the negative electrode pressing step is low. In addition, the secondary batteries of Examples 1 to 4 had the following advantages: 1. The secondary batteries of Comparative Example 2 including a negative electrode including a two-dimensional porous body having a smaller porosity than the above range as a current collector. It can be seen that a decrease in discharge capacity when discharging at a high rate such as 0C can be suppressed.

In the above-described embodiment, a polymer lithium secondary battery having a unit cell having a five-layer structure in which a positive electrode, an electrolyte layer, a negative electrode, an electrolyte layer, and a positive electrode are stacked in this order has been described as an example. Is not limited to such a five-layer structure. For example, a positive electrode, a negative electrode, and an electrolyte layer may be used one by one to form a three-layer structure.

[0063]

As described above in detail, according to the present invention, it is possible to provide a polymer lithium secondary battery having improved high-rate discharge characteristics while maintaining excellent mass productivity.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a polymer lithium secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Negative electrode, 3 ... Electrolyte layer, 4 ... Positive electrode collector, 5 ... Positive electrode layer, 6 ... Negative electrode current collector, 7 ... Negative electrode layer, 11 ... Exterior film.

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Claims (2)

[Claims] 1. A negative electrode having a tensile strength of 4 N / mm ² or more, a porosity of 40 to 80%, and a current collector containing a two-dimensional porous body made of copper or a copper alloy. Polymer lithium secondary battery. 2. A polymer lithium secondary battery having a negative electrode obtained by applying a paste containing an active material and a polymer having a property of retaining a nonaqueous electrolyte solution to a current collector and pressing the paste. A polymer lithium secondary battery, wherein the electric body is a two-dimensional porous body having a tensile strength of 4 N / mm ² or more, a porosity of 40 to 80%, and copper or a copper alloy.